In the early 1990s, the Tunisian regime jailed several thousand members of the Islamist movement Ennahda, sentencing them to long prison terms in which they faced routine brutality and isolation. The movement was thought to be at an end. Yet the paradox of Tunisian Islamism is that not only did Ennahda emerge from two decades of repression as the strongest political force in the country, but also that the movement had gone through a long, private process of ideological revision that prefigured its accommodationist stance in the post-2011 transition. I ask what was the effect of the repression of prison on the movement’s development? This paper excavates the experience of Ennahda prisoners in Ben Ali’s jails to explain practices of coercion, the nature of discussions over the movement’s actions in the clash with the regime, and the gradual emergence of acts of resistance to the prison authorities and the reclaiming of individual dignity despite the weight of repression. This draws on a year of ethnographic fieldwork among Ennahda members in Tunisia as part of a broader project about the movement’s evolution. Scholars have shown how integration in the political process can in some situations ‘moderate’ Islamist movements to adopt a more tolerant ideology, through the boundary-shifting effect of political action (Schwedler 2006). Conversely, others argue that repression too can sometimes ‘force’ Islamist parties to moderate their policies (Hamid 2014). I argue in this paper that there is evidence in the case of Ennahda of lasting ideological and strategic revision that occurred during a period of intense repression. However, there is also evidence here of profound and as yet unresolved disagreements between ordinary members and the movement’s leadership, particularly those who escaped into exile abroad who sought to defend their record. In Tunisia’s democratic transition since 2011 the Islamist movement Ennahda has adopted a cautious approach, compromising its religious ambitions and reaching agreements with political rivals in the name of consensus. Some have suggested Ennahda has acted out of fear of repeating the mistakes of the Muslim Brothers in Egypt. I argue in this paper, however, that the legacy of the prison-era evaluations inside Tunisia best explains the strategies Ennahda has adopted since the uprising of 2011, as well as explaining the movement’s resilience during two decades of repression.